The present invention relates to breathing apparatus for protecting crew members, in particular the technical flight crew, of an airplane against the risks associated with depressurization at high altitude and/or the occurence of smoke in the cockpit.
A major, although non-exclusive application lies in passenger airliners that can reach high altitudes, and above all so-called “jumbo” or “super-jumbo” aircraft of very large capacity.
At present, each airliner pilot has breathing apparatus comprising a mask fitted with a demand regulator connected to a source of breathing gas. Aviation regulations require that the mask can be put into place and supply oxygen to its wearer in less than 5 seconds. At present, this result is generally achieved by using a mask with a pneumatic harness that can be inflated and deflated, such as one of those described in documents FR-A-1 506 342 (or GB 1175080), FR-A-2 784 900, and U.S. Pat. No. 5,623,923, the content of which is incorporated herein by way of reference. The source of gas under pressure must be capable of instantly delivering oxygen or air greatly enriched in oxygen at a pressure which is sufficient for inflating the harness and feeding the regulator of the mask. In general, the source is a cylinder of oxygen under pressure.
On airliners, another installation is provided to supply passengers with breathing gas in the event of depressurization and to ensure survival until the airplane has come down to an altitude where normal breathing is possible at ambient atmospheric pressure.
On passenger “jumbos”, the necessary supply of oxygen requires a very large weight.
In order to reduce this mass, the oxygen supply can be replaced by an on board oxygen generator, such as a battery of on-board oxygen generator systems (OBOGS) fed with air derived from the compressor of one or more of the engines. However, such generators supply air that is highly enriched in oxygen only after a delay has elapsed from the command to supply oxygen. In addition, the output pressure of an OBOGS depends on the rotational speed of the engine and the air supplied is enriched in oxygen to a degree that is variable. The pressure initially available can be too low to inflate the fast-donning harness. The initial degree of enrichment can also be insufficient. A common buffer tank for acting as a supply of very enriched air is placed at the outlet of the OBOGS, but that solution is far from perfect, particularly since the available pressure can be insufficient for inflating a harness and since the presence of an oxygen transfer pipe causes a further delay. Other types of on-board generator and even common oxygen supplies present similar drawbacks.